eli5; Why do different substances have different heat capacities?

Question

Basically the title: but what about a substance makes it makes it’s specific heat capacity higher or lower than another? From what I understand, SHC is the amount of energy absorbed by a substance in order for it to be raised by 1C. But on a molecular level, what determines this and why is it different between different substances or different states of a substance? eg liquid water has SHC of 4.184J/JC, ice has SPC of 2.11J/JC and vapour has SPC of 2J/JC. Very convoluted question but an explanation would be greatly appreciated 🙂

In: 1

Answer 1

Even though different molecules are not bonded together like the atoms in each molecule, there are intermolecular forces between molecules. This is what keeps solids solid. In liquids, these forces keep the molecules together but only loosely. In gases, the intermolecular forces are too weak to keep the molecules close to each other.

In the specific case of a water molecule, there’s two hydrogen atoms and an oxygen atom that are bonded together in the shape of the letter V. Even though the molecule as a whole is electrically neutral, the oxygen atom in a water molecule has some negative charge while the hydrogen atoms have positive charges. Because of this, the oxygen atoms of each water molecule are attracted to the hydrogen atoms of other water molecules. This is called electrostatic force.

Now, temperature describes the average amount of kinetic energy particles have within a substance. Basically, the more the particles vibrate and bounce around, the larger temperature we measure. Forces like electrostatic force make it more difficult for molecules to move around, so we need to use more energy to make them move. Specific heat capacity tells us how much energy we need to make those particles move a specific amount more than they already were moving.

Also, since temperature description the *average* amount of kinetic energy particles have, denser substances generally have higher specific heat capacity simply because there’s more particles in them and all of them require energy to move faster.